One common characteristic of biological samples, such as cell and tissue lysates, serum samples etc. and other complex samples of molecules, is that the molecules comprised in these samples are not represented equally in terms of their relative abundance. For example, albumin constitutes about 50% of the protein in total serum whereas transthyretin constitutes about 0.3%.
One consequence is that, notwithstanding the many techniques for separation of samples of molecules, where two or more molecules have a common characteristic and are separated according to that characteristic, it is difficult to distinguish one molecule from the other. Importantly, it is difficult, and may well indeed be impossible, to detect the molecule that has the lower relative abundance. For example, where molecules are separated according to molecular weight and charge in 2 dimensional gel electrophoresis, it is very difficult to detect a molecule having a low relative abundance in the sample in the circumstance where a molecule having a high relative abundance and the same or similar molecular weight and charge is also present in the sample.
Thus a limitation applies to the applicability of techniques such as 2 dimensional gel electrophoresis for permitting identification of molecules that have a low relative abundance in a sample. This limitation is a significant barrier to the discovery of molecules in fields such as proteomics.
One approach to improving the capacity of 2 dimensional gel electrophoresis for identification of proteins is to deplete molecules from a sample that have a high relative abundance by selecting known or otherwise commercially available antibodies to deplete proteins having a high relative abundance before 2 dimensional gel electrophoresis.
A problem with this approach is that the depletion of high abundance proteins is limited by the content of the panel of known or otherwise commercially available antibodies available for selection. Accordingly, the only high relative abundance proteins that can be depleted are those for which the antibodies are known or are otherwise commercially available. Further, proteins that have a lower relative abundance than those depleted by this approach, and that have a higher relative abundance than the protein of interest, may not be depleted if the antibodies for binding to these proteins are not available.
A further problem is that in many biological fluids, the proteins that have the higher relative abundance may not be known or otherwise, no antibodies may be available to bind to these. Accordingly it is not possible to deplete the proteins having a high relative abundance from these samples using this approach.
Another problem with this approach is that it is expensive and requires a degree of technical manipulation to prepare the known or otherwise commercially available antibodies to be used for depletion. While depletion would be assisted by using antibodies that bind to different epitopes of the same protein, in practice it is very difficult to prepare a composition including more than one antibody for each protein to be depleted, for the depletion of more than one high abundance protein.
There is a need for an improvement in the identification or detection of molecules that have a low relative abundance in a sample.